North of Yakutat within Wrangell–St. Elias National Park, spectacular Hubbard Glacier is the largest tidewater glacier in North America. Fed by high mountains of the St. Elias Range, the glacier is six miles wide and more than 70 miles long. Many cruise ships make a stop in front of this massive glacier with an always-calving 400-foot-high wall of ice. Local air taxis offer flightseeing trips that provide an even more impressive glacier view.

Virtually all Alaskan glaciers are retreating as the global climate warms, but Hubbard Glacier is the rare exception. Not only is it advancing, but doing so in a way that threatens to block off the waters of Russell Fiord (yes, “fiord” is the official spelling). Today, just 100 yards of open water separate the ice from a rocky point of land at Point Gilbert.

If the glacier continues advancing, the gap could close, creating a dam that drastically changes the surrounding landscape. This occurred in 1986 when the water rose 75 feet behind an ice dam, trapping seals, sea lions, and porpoises. The ice gave way six months later, freeing the animals and reconnecting the fiord to Disenchantment Bay.

A similar situation developed in 2002, and scientists believe it is only a matter of time until ice from the surging glacier creates a relatively permanent dam. If this happens, water would eventually flood the Situk River, potentially impacting the river’s acclaimed steelhead trout, not to mention the airport.

Visit the U.S. Geological Survey website (http://ak.water.usgs.gov) for more on the Hubbard.